(i) Field of the Invention
The present invention relates to the modulation of α-secretase and cognitive enhancement. The invention further relates to compounds for treatment of conditions associated with amyloid processing such as Alzheimer's Disease and compositions for the treatment of such conditions.
(ii) Background of the Invention
Various disorders and diseases exist which affect cognition. Cognition can be generally described as including at least three different components: attention, learning, and memory. Each of these components and their respective levels affect the overall level of a subject's cognitive ability. For instance, while Alzheimer's Disease patients suffer from a loss of overall cognition and thus deterioration of each of these characteristics, it is the loss of memory that is most often associated with the disease. In other diseases patients suffer from cognitive impairment that is more predominately associated with different characteristics of cognition. For instance Attention Deficit Hyperactivity Disorder (ADHD), focuses on the individual's ability to maintain an attentive state. Other conditions include general dementias associated with other neurological diseases, aging, and treatment of conditions that can cause deleterious effects on mental capacity, such as cancer treatments, stroke/ischemia, and mental retardation.
Cognition disorders create a variety of problems for today's society. Therefore, scientists have made efforts to develop cognitive enhancers or cognition activators. The cognition enhancers or activators that have been developed are generally classified to include nootropics, vasodilators, metabolic enhancers, psychostimulants, cholinergic agents, biogenic amine drugs, and neuropeptides. Vasodilators and metabolic enhancers (e.g. dihydroergotoxine) are mainly effective in the cognition disorders induced by cerebral vessel ligation-ischemia; however, they are ineffective in clinical use and with other types of cognition disorders. Of the developed cognition enhancers, typically only metabolic drugs are employed for clinical use, as others are still in the investigation stage. Of the nootropics for instance, piracetam activates the peripheral endocrine system, which is not appropriate for Alzheimer's disease due to the high concentration of steroids produced in patients while tacrine, a cholinergic agent, has a variety of side effects including vomiting, diarrhea, and hepatotoxicity.
Ways to improve the cognitive abilities of diseased individuals have been the subject of various studies. Recently the cognitive state related to Alzheimer's Disease and different ways to improve patient's memory have been the subject of various approaches and strategies. Unfortunately, these approaches and strategies only improve symptomatic and transient cognition in diseased individuals but have not addressed the progression of the disease. In the case of Alzheimer's Disease, efforts to improve cognition, typically through the cholinergic pathways or though other brain transmitter pathways, have been investigated. The primary approach relies on the inhibition of acetyl cholinesterase enzymes through drug therapy. Acetyl cholinesterase is a major brain enzyme and manipulating its levels can result in various changes to other neurological functions and cause side effects.
While these and other methods may improve cognition, at least transiently, they do not modify the disease progression, or address the cause of the disease. For instance, Alzheimer's Disease is typically associated with the formation of plaques through the accumulation of amyloid precursor protein. Attempts to illicit an immunological response through treatment against amyloid and plaque formation have been done in animal models, but have not been successfully extended to humans.
Furthermore, cholinesterase inhibitors only produce some symptomatic improvement for a short time and in only a fraction of the Alzheimer's Disease patients with mid to moderate symptoms and are thus only a useful treatment for a small portion of the overall patient population. Even more critical is that present efforts at improving cognition do not result in treatment of the disease condition, but are merely ameliorative of the symptoms. Current treatments do not modify the disease progression. These treatments have also included the use of a “vaccine” to treat the symptoms of Alzheimer's Disease patients which, while theoretically plausible and effective in mice tests, have been shown to cause severe adverse reactions in humans.
As a result, use of the cholinergic pathway for the treatment of cognitive impairment, particularly in Alzheimer's Disease, has proven to be inadequate. Additionally, the current treatments for cognitive improvement are limited to specific neurodegenerative diseases and have not proven effective in the treatment of other cognitive conditions.
Alzheimer's disease is associated with extensive loss of specific neuronal subpopulations in the brain with memory loss being the most universal symptom. (Katzman, R. (1986) New England Journal of Medicine 314:964). Alzheimer's disease is well characterized with regard to neuropathological changes. However, abnormalities have been reported in peripheral tissue supporting the possibility that Alzheimer's disease is a systemic disorder with pathology of the central nervous system being the most prominent. (Connolly, G., Fibroblast models of neurological disorders: fluorescence measurement studies, Review, TiPS Vol. 19, 171-77 (1998)). For a discussion of Alzheimer's disease links to a genetic origin and chromosomes 1, 14, and 21 see St. George-Hyslop, P. H., et al., Science 235:885 (1987); Tanzi, Rudolph et al., The Gene Defects Responsible for Familial Alzheimer's Disease, Review, Neurobiology of Disease 3, 159-168 (1996); Hardy, J., Molecular genetics of Alzheimer's disease, Acta Neurol Scand: Supplement 165: 13-17 (1996).
While cellular changes leading to neuronal loss and the underlying etiology of the disease remain under investigation the importance of APP metabolism is well established. The two proteins most consistently identified in the brains of patients with Alzheimer's disease to play a role in the physiology or pathophysiology of brain are β-amyloid and tau. (See Selkoe, D., Alzheimer's Disease: Genes, Proteins, and Therapy, Physiological Reviews, Vol. 81, No. 2, 2001). A discussion of the defects in β-amyloid protein metabolism and abnormal calcium homeostasis and/or calcium activated kinases. (Etcheberrigaray et al., Calcium responses are altered in fibroblasts from Alzheimer's patients and pre-symptomatic PS1 carriers: a potential tool for early diagnosis, Alzheimer's Reports, Vol. 3, Nos. 5 & 6, pp. 305-312 (2000); Webb et al., Protein kinase C isozymes: a review of their structure, regulation and role in regulating airways smooth muscle tone and mitogenesis, British Journal of Pharmacology, 130, pp 1433-52 (2000)).
Further with regard to normal and abnormal memory both K+ and Ca2+ channels have been demonstrated to play key roles in memory storage and recall. For instance, potassium channels have been found to change during memory storage. (Etcheberrigaray, R., et al. (1992) Proceeding of the National Academy of Science 89:7184; Sanchez-Andres, J. V. and Alkon, D. L. (1991) Journal of Neurobiology 65:796; Collin, C., et al. (1988) Biophysics Journal 55:955; Alkon, D. L., et al. (1985) Behavioral and Neural Biology 44:278; Alkon, D. L. (1984) Science 226:1037). This observation, coupled with the almost universal symptom of memory loss in Alzheimer's patients, led to the investigation of potassium channel function as a possible site of Alzheimer's disease pathology and the effect of PKC modulation on cognition.
PKC was identified as one of the largest gene families of non-receptor serine-threonine protein kinases. Since the discovery of PKC in the early eighties by Nishizuka and coworkers (Kikkawa et al., J. Biol. Chem., 257, 13341 (1982), and its identification as a major receptor for phorbol esters (Ashendel et al., Cancer Res., 43, 4333 (1983)), a multitude of physiological signaling mechanisms have been ascribed to this enzyme. The intense interest in PKC stems from its unique ability to be activated in vitro by calcium and diacylglycerol (and its phorbol ester mimetics), an effector whose formation is coupled to phospholipid turnover by the action of growth and differentiation factors.
The PKC gene family consists presently of 11 genes which are divided into four subgroups: 1) classical PKCα, β1, β2 (β1 and β2 are alternatively spliced forms of the same gene) and γ, 2) novel PKCδ, ε, η and θ, 3) atypical PKCξ, λ, η and ι and 4) PKCμ. PKCμ resembles the novel PKC isoforms but differs by having a putative transmembrane domain (reviewed by Blohe et al., Cancer Metast. Rev., 13, 411 (1994); Ilug et al., Biochem j., 291, 329 (1993); Kikkawa et al., Ann. Rev. Biochem. 58, 31 (1989)). The α, β1, β2, and γ isoforms are Ca2+, phospholipid and diacylglycerol-dependent and represent the classical isoforms of PKC, whereas the other isoforms are activated by phospholipid and diacylglycerol but are not dependent on Ca2+. All isoforms encompass 5 variable (V1-V5) regions, and the α, β, γ isoforms contain four (C1-C4) structural domains which are highly conserved. All isoforms except PKCα, β and γ lack the C2 domain, and the λ, η and isoforms also lack nine of two cysteine-rich zinc finger domains in C1 to which diacylglycerol binds. The C1 domain also contains the pseudosubstrate sequence which is highly conserved among all isoforms, and which serves an autoregulatory function by blocking the substrate-binding site to produce an inactive conformation of the enzyme (House et al., Science, 238, 1726 (1987)).
Because of these structural features, diverse PKC isoforms are thought to have highly specialized roles in signal transduction in response to physiological stimuli (Nishizuka, Cancer, 10, 1892 (1989)), as well as in neoplastic transformation and differentiation (Glazer, Protein Kinase C, J. F. Kuo, ed., Oxford U. Press (1994) at pages 171-198). For a discussion of known PKC modulators see PCT/US97/08141, U.S. Pat. Nos. 5,652,232; 6,043,270; 6,080,784; 5,891,906; 5,962,498; 5,955,501; 5,891,870 and 5,962,504.
In view of the central role that PKC plays in signal transduction, PKC has proven to be an exciting target for the modulation of APP processing. It is well established that PKC plays a role in APP processing. Phorbol esters for instance have been shown to significantly increase the relative amount of non-amyloidogenic soluble APP (sAPP) secreted through PKC activation. Activation of PKC by phorbol ester does not appear to result in a direct phosphorylation of the APP molecule, however. Irrespective of the precise site of action, phorbol-induced PKC activation results in an enhanced or favored α-secretase, non-amyloidogenic pathway. Therefore PKC activation is an attractive approach for influencing the production of non-deleterious sAPP and even producing beneficial sAPP and at the same time reduce the relative amount of Aβ peptides. Phorbol esters, however, are not suitable compounds for eventual drug development because of their tumor promotion activity. (Ibarreta, et al., Benzolactam (BL) enhances sAPP secretion in fibroblasts and in PC12 cells, NeuroReport, Vol. 10, No. 5&6, pp 1035-40 (1999)).
There is increasing evidence that the individual PKC isozymes play different, sometimes opposing, roles in biological processes, providing two directions for pharmacological exploitation. One is the design of specific (preferably, isozyme specific) inhibitors of PKC. This approach is complicated by the fact that the catalytic domain is not the domain primarily responsible for the isotype specificity of PKC. The other approach is to develop isozyme-selective, regulatory site-directed PKC activators. These may provide a way to override the effect of other signal transduction pathways with opposite biological effects. Alternatively, by inducing down-regulation of PKC after acute activation, PKC activators may cause long term antagonism. Bryostatin is currently in clinical trials as an anti-cancer agent. The bryostatins are known to bind to the regulatory domain of PKC and to activate the enzyme. Bryostatin is an example of isozyme-selective activators of PKC. Compounds in addition to bryostatins have been found to modulate PKC. (see for example WO 97/43268)
There still exists a need for the development of methods for the treatment for improved overall cognition, either through a specific characteristic of cognitive ability or general cognition. There also still exists a need for the development of methods for the improvement of cognitive enhancement whether or not it is related to specific disease state or cognitive disorder. The methods and compositions of the present invention fulfill these needs and will greatly improve the clinical treatment for Alzheimer's disease and other neurodegenerative diseases, as well as, provide for improved cognitive enhancement. The methods and compositions also provide treatment and/or enhancement of the cognitive state through the modulation of α-secretase.